Cigarette smoking is the leading cause of mortality in the U.S., resulting in over 480,000 deaths every year and costing more than $300 billion in loss of productivity. Smoking is also the leading cause of cancer and of deaths from cancer. Smoking causes cancers of the lung, larynx, mouth, bladder, liver, kidney, colon, rectum and others. While smoking rates in the U.S. have declined over recent years to 16.8%, decreases in smoking rates have been relatively slow since 1990, and the problem of relapse remains a major obstacle to reducing smoking prevalence. Only about 4% of those attempting to quit on their own and 15 to 25% of those involved in intensive cessation treatments remain abstinent as long as one year. Thus, the development of innovative and efficacious behavioral and pharmacological approaches to smoking cessation treatment remains a significant public health priority. Tobacco quitlines are the major vehicle through which smoking cessation services are delivered in the U.S and are available in every U.S. state via a national quitline portal, 1-800-QUIT-NOW. Quitline counseling, for smokers initiating calls to quitlines, has impressive odds ratios of 1.20 to 1.66 in the latest Cochrane meta- analysis, however, the actual quit rates from the meta-analysis ranged only from 5% to 14%, or 21% when NRT was offered. Calls for new methods of improving tobacco quitline outcomes are clearly warranted. Within the field of behavioral psychology, positive psychology has been a burgeoning area of research that may provide valuable and innovative directions for improving on behavioral smoking cessation treatments. Our investigative team recently developed and tested a smoking cessation treatment that incorporates training in positive psychology intervention strategies, which resulted in significantly higher odds of smoking abstinence across 26 weeks of follow-up compared to standard behavioral treatment. These promising findings suggest that providing tobacco quitline users with training and practice in the use of positive psychology skills during the course of their quitline engagement may increase smoking cessation outcomes relative to standard quitline use. Tobacco quitlines would derive significant benefit from such an adjunctive psychosocial approach for their clients. While issues of feasibility limit the use of this approach in a standard delivery method, its use in the form of a mobile application (app) holds significant promise. The aims of this Phase I application are to employ user centered design processes to develop and test the acceptability and efficacy of a mobile health app, pQuit, which will incorporate intervention strategies from the field of positive psychology vs. a relaxation app, Breathe2Relax in a small randomized controlled trial of adult smokers. All participants will receive tobacco quitline counseling. The expected outcome of this project is the development of a prototype of pQuit, which can readied for Phase II testing of clinical efficacy in a future randomized controlled trial in conjunction with tobacco quitline counseling.